This circuit is
an oscillator
that generates a square wave. The op-amp
starts with its two inputs in an unknown state; let's say it starts
with + slightly higher than –. The op-amp greatly amplifies
this difference, bringing its output to the op-amp's
positive power supply voltage, its maximum output (15 V in this
case). The two 100k resistors act as a voltage divider which put the +
input at half the output voltage, or 7.5 V. The – input is at
ground, lower than the + input, so the op-amp output stays at 15 V.

Current flows from the op-amp output to ground through the capacitor,
charging it. As soon as it charges to slightly more than 7.5 V, the
– input is now higher than the +, and so the output flips to -15
V. This brings the + input to -7.5 V.

Now current flows in the other direction, discharging the capacitor
and reversing its polarity until it reaches -7.5 V. Then the cycle repeats.